Conventional techniques are used in large scale integrated circuit chips, such as system-on-chip (SOC) devices, to provide different transistor devices with different voltage thresholds (hereinafter “Vt”). One reason is to reduce power consumption. For example, high Vt (hereinafter “HVT”) devices may be used where timing is not a critical concern. On the other hand standard Vt (hereinafter “SVT”) and low Vt (hereinafter “LVT) device may be used where timing is a critical concern. One conventional technique for varying the Vt in transistor devices is to vary the channel doping. However, the conventional technique of varying Vt by varying channel doping can have shortcomings. One is that is in smaller devices, such as FinFETs, the channel doping may provide a lower than desired range of Vt tuning. Another manifestation, particularly in FinFETs, can be a random dopant fluctuation, e.g., due to fabrication tolerances. The random dopant variation may cause unwanted variance in channel mobility, including an increase percentage of devices having unacceptable channel mobility.
One pursuit of a solution is to find a means to control the work-function of the gate. One conventional technique is to fabricate the gates of devices using different work-function metals. For example, one work-function metal may be used in the gate LVT devices, another in the gate of SVT devices, and still another in the gate of HVT devices. This conventional technique may be termed a “conventional multi work-function metal” technique. The conventional multi work-function metal technique, however, can have substantial shortcomings, such as a significant increase in complexity and cost of fabrication.